Hunter syndrome definition and facts
- Hunter syndrome is a genetic disease caused by a deficient or absent enzyme that is X-linked recessive. Hunter syndrome occurs mainly in males and produces symptoms starting at ages 2 to 4 years.
- Symptoms of Hunter syndrome range from mild to severe and may include the following:
- Facial changes
- Head enlargement
- Abnormal bone size and shapes
- Tongue protrusion
- Voice changes
- Joint stiffness
- Small growths on skin
- Distended abdomen
- Enlarged internal organs
- Developmental delays (physical and mental)
- The cause of Hunter syndrome is due to an abnormal X chromosome that males usually inherit from the mother.
- The two major risk factors for Hunter syndrome are a mother with an abnormal X chromosome, and her offspring is male.
- A large number of pediatric specialists may treat a child with Hunter syndrome because of the wide range of symptoms that can develop. If the child lives to adulthood, similar specialists may be involved in care for the adult with Hunter syndrome.
- Hunter syndrome is sometimes difficult to diagnose. Early symptoms include facial changes, and the definitive diagnosis depends on the genetic analysis of the child's X chromosome.
- Treatment for Hunter syndrome is mainly confined to reducing symptoms or slowing symptom development with idursulfase (Elaprase). There is no cure for Hunter syndrome.
- Complications of Hunter syndrome can involve all of the organ systems, including respiratory, skeletal, connective tissue, cardiac, and brain (neurologic).
- Life expectancy for individuals with Hunter syndrome ranges from about 10 to 20 years of age.
- There are two other terms that are sometimes confused with Hunter syndrome: 1) Bow Hunter Syndrome; and 2) Hurler Hunter syndrome (mucopolysaccharidosis I and MPS I), an inherited disease that produces similar symptoms and outcomes to Hunter syndrome.
What is Hunter syndrome?
Hunter syndrome is a very rare X - linked recessive inherited disease. Hunter
syndrome is a lysosomal storage disease caused by deficient or absent enzyme,
iduronate-2-sulfatase (I2S). This causes the accumulation of heparin sulfate and dermatan sulfate to accumulate in body tissues. Injury to various organs
lead to the symptoms from the disease. Hunter syndrome is also termed
Mucopolysaccharidosis II or MPS II.
4 Types of Genetic Diseases
There are a number of different types of genetic inheritance, including the following four modes:
- Single gene inheritance (cystic fibrosis, sickle cell anemia)
- Multifactoral inheritance (heart disease, cancer)
- Chromosome abnormalities (Down syndrome)
- Mitochondrial inheritance (epilepsy, a type of dementia)
What are the signs symptoms of Hunter syndrome?
The symptoms of Hunter syndrome usually are not present at birth, but begin in
young children ages about 2-4, and may range from mild to severe. Symptoms
- Facial changes such as thickening of
the lips, nostrils flaring and broadening of the nose
- Head enlargement (macrocephaly)
- Tongue protrusion
- Hoarseness and/or deepening of the
- Changes in the bones produces abnormal
bone size and/or bone shape
- Joint stiffness
- Small whitish growths on the skin
- Enlarged internal organs
- Distended abdomen
- Delayed development (for example, child
does not meet normal development such as talking or normal motor skills like
- Behavior that becomes aggressive
- Reduced or stunted growth
What causes Hunter syndrome?
The cause of Hunter syndrome is an abnormal gene X chromosome that is inherited from the mother. This genetic abnormality allows mucopolysaccharides to accumulate in large amounts in cells, the blood and in connective tissues. This accumulation causes damage to cells and organs. It is a progressive disease that usually causes a shortened lifespan and major developmental abnormalities. Hunter syndrome occurs almost exclusively in males.
Who gets Hunter syndrome?
The two major risk factors for Hunter syndrome are a family history of Hunter syndrome, and being male, since predominantly males are affected. Females rarely get the disease because they inherit two X chromosomes so that even if one is defective, the other X chromosome with functioning genes usually can compensate for the abnormality.
Which specialties of doctors treat Hunter syndrome?
There are a number of physician specialties that may treat Hunter syndrome.
Treatment is geared toward managing the symptoms and complications of the
disease. There is no cure
for this progressive disease. Specialties of physicians that may be involved in
caring for persons with Hunter syndrome include pediatric pulmonologists,
critical-care specialists, emergency medicine specialists, orthopedists,
geneticists, rheumatologists, internal medicine specialists, neurologists,
surgeons and child psychologists. If the child survives to adulthood, similar
specialists that treat adults may be consulted.
How is Hunter syndrome diagnosed?
The diagnosis of Hunter syndrome is sometimes difficult because of its slow
onset and overlapping symptoms with other childhood problems. Early signs that
suggest a diagnosis include facial changes in the child. The pediatrician then
usually completes a detailed personal family history and physical examination of
the individual. Blood, urine, and/or tissue samples can be tested for either the
deficient enzyme or excess mucopolysaccharides. Definitive diagnosis is done by
a genetic analysis of the child's X chromosome(s). There is no routine newborn
screening available to diagnose Hunter syndrome. However, in families with known
Hunter syndrome, prenatal testing of the amniotic fluid or placental tissue may
be available and can verify the diagnosis in a fetus.
What is the treatment for Hunter syndrome?
Currently, treatment is geared toward managing symptoms and complications as there is no cure for this progressive disease. Treatments depend on the organ(s) involved and can include assistance with breathing, physical therapy to maintain functions, drainage of fluids to build up in the brain and/or spinal cord, heart valve replacement and other treatments such as behavior management. Some physicians utilize specific enzyme therapy to replace child's deficient enzymes. The treatment is termed enzyme replacement therapy (ERT) using an IV – infused enzyme (Elaprase). It is still being refined along with gene therapy to replace the abnormal part of the X chromosome.
What are the complications of Hunter syndrome?
Complications of Hunter syndrome are:
- Respiratory complications (thickened
tongue can obstruct breathing)
- Skeletal problems (abnormal bone
development and joint problems)
- Connective tissue (accumulation of
mucopolysaccharides can cause swelling)
- Heart (thickened tissue resulting in
- Brain (hydrocephalus)
- Nervous system (thickened membranes
impede nerve functions)
- Reduced ability to recover from most
What is the life-expectancy for a person with Hunter syndrome?
The life expectancy the person with Hunter syndrome is reduced and ranges
from about 10 to 20 years of age. However, with mild disease, some individuals live into
adulthood. Obstruction of breathing or heart disease are the major causes of
What are other names for Hunter syndrome?
Hunter syndrome is also known as
- Mucopolysaccharidosis II,
- MPS II, and
Some researchers use subtypes such as MPS IIA and MPS IIB (MPS IIA
is severe disease while MPS IIB is mild disease).
There are two other terms that are sometimes confused with Hunter syndrome.
- The first is Bow Hunter Syndrome, a problem when a person rotates their head and
causes circulation ischemia in the dominant vertebral artery that produces
vertigo, nystagmus and
ataxia (inability to walk normally).
second term is Hurler Hunter syndrome. This term also is known as Hurler
syndrome (mucopolysaccharidosis I and MPS I), and is closely related to Hunter
syndrome because it also is an inherited disease that results in a lack of an
enzyme called alpha- L-iduronidase, which produces similar symptoms and
outcomes to Hunter syndrome.
Medically Reviewed on 12/4/2018
Medically reviewed by Larry C. Deeb, MD; American Board of Pediatric Endocrinology
Bitar, T., MD. "Mucopolysaccharidosis." Medscape. Updated Feb 02, 2016.
U.S. National Library of Medicine; Genetics Home Reference. "mucopolysaccharidosis type II." Updated June 28, 2016.
National Organization for Rare Disorders. "Mucopolysaccharidosis Type II."